Lower limb
Sciatic nerve
Nervus ischiadicus
- Origin
- Largest nerve in the human body, arising from the sacral plexus anterior rami (L4, L5, S1, S2, S3)
- Insertion
- Exits the pelvis via the infrapiriform foramen, descends between the greater trochanter and ischial tuberosity down the posterior thigh, bifurcating above the popliteal fossa into tibial and common fibular nerves
- Function
- Motor to hamstring muscles (semitendinosus, semimembranosus, biceps femoris) and hamstring part of adductor magnus; supplies all leg and foot muscles via terminal branches; sensory to posterior thigh and entire leg/foot except medial skin
- Innervation
- Major mixed nerve comprising distinct tibial and common fibular divisions within a common connective tissue sheath
- Movement & chain
- Tensioned dramatically during combined hip flexion and knee extension
- Palpation
- Palpable midway between the ischial tuberosity and greater trochanter beneath gluteus maximus
- Clinical
- Sciatica (radicular nerve pain from L5/S1 herniated disc), piriformis syndrome, iatrogenic injury from misplaced intragluteal injections or posterior hip dislocation
- Segmental innervation
- L4, L5, S1, S2, S3 spinal cord roots
- In clinical practice
- Straight Leg Raise (Lasègue's sign) for root tension; ventrogluteal (von Hochstetter) injection site protocol to prevent catastrophic sciatic nerve trauma
- Region in the model
- Lower limb